The present invention relates to a semiconductor device and control method, and relates in particular to power reduction during standby mode in the physical layer block for the serial data communication interface and power reduction in the standby mode state in the physical layer block conforming to USB 3.0 standards.
There are steadily increasing demands for reducing power in products centering on portable devices. Lowering power consumption during normal operation and standby mode operation is also important in the development of the physical layers of serial data communication interfaces.
FIG. 1 is a drawing showing the characteristics of the link states (U0 mode through U3 mode) in USB 3.0. Referring to FIG. 1 shows that the link states in the USB.3.0 standards are grouped into a normal mode state (U0 mode) and multiple standby mode states (U1 mode-U3 mode) and that fine power control is specified for each state. The power in particular in the standby mode state in U3 mode requires an average current of 2.5 mA or less.
In power regulation in USB 3.0, low power consumption during standby mode is achieved by stopping operation of all unnecessary circuit blocks depend on each standby mode state.
As shown in FIG. 2, a LFPS (Low Frequency Periodic Signaling) signal is utilized between the USB 3.0 A (host) 100 and the USB 3.0 B (device) 200 connected in 1-to-1 relationship to implement recovery operation from standby mode state (U1 mode-U3 mode) to the normal mode state (U0 mode).
FIG. 3 is a diagram of the signal exchange between the host 100 and the device 200 during recovery from the standby mode state. The LFPS signal is also sent from the opponent during standby mode. The LFPS detector must therefore be operating even when in standby mode state in order to constantly monitor the LFPS signals sent from the opponent.
The frequency of the LFPS signal is 10 to 50 MHz which is a frequency much lower than the data transfer speed of 5 Gbps during normal mode operation in USB 3.0. The LFPS detector can therefore achieve relatively low power consumption. However, achieving accuracy between 100-300 mV as the standard for the amplitude detection threshold of the LFPS signal requires contriving an LFPS detector for detecting LFPS signals as shown in the circuit example in FIG. 4 by utilizing current mode logic (CML) type circuits. Reducing the current consumption in the detector to zero is therefore impossible.
Moreover, when there are multiple USB 3.0 lanes, then setting the average current below 2.5 mA during standby mode in U3 mode at the device level requires drastically reducing the power by cutting power consumption in the physical layer block containing the LFPS detector. Also when lowering the power consumption in standby mode state in devices conforming to USB 3.0 standards, then low power consumption must be attained while maintaining the detection threshold accuracy of the LFPS circuit.
Technology for monitoring signals at minimal power consumption is disclosed for example in Japanese Unexamined Patent application Publication No. 2000-284867 in which a USB device contains an infrared communication module, and a microcomputer intermittently (periodically) operates the infrared module for a specified period during standby mode so that the infrared signal is monitored at minimal power consumption and the infrared module is returned to the normally active state when an infrared signal is detected.